1. Field of the Invention
The present invention relates to pneumatic discharge arrangements for unloading lading from a transportation vehicle having a discharge hopper, such as a railway hopper car.
2. Description of the Prior Art
Pneumatic discharge arrangements for removing lading from a hopper are old and well-known. Pneumatic discharge for a hopper is particularly useful for lading materials that are particulate, granular, or pelletized, such as plastic pellets.
Various designs have been developed for this purpose. Usually, a control tube is supported below a tapering hopper. An opening in the lower portion of the hopper communicates with the control tube. A valve opens and closes the opening. When open, the valve allows lading to fall through the hopper into the control tube where it is drawn out by a vacuum intake connected thereto.
The lading may rest heavily on the valve, and the force required for an operator to initially move the valve may be quite considerable. Therefore, it is desirable to provide a relatively high mechanical advantage to the operator at this point in operation. Earlier designs provided for movement of the valve using rack-and-pinion arrangements which were vulnerable to misalignment and provided relatively little mechanical advantage to an operator initially opening and closing the valve.
In the prior art, the control tube is covered by caps which are hingedly supported on the hopper structure. Latches secure the caps when the control tube is sealed. It is desirable from the viewpoint of efficiency to provide a structure where the unlatching and pivoting of the cap is accomplished by a single operator action. The prior art latches are relatively complicated and do not provide this simplicity of action.
Also, the control tubes of older designs may be sealed while the gate is open. This risks the possibility of the hopper being filled while the gate is open which renders pneumatic unloading difficult or impossible due to the fact that the control tube becomes blocked and air flow therethrough cannot be readily established.